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11th West Bengal Board

IMPORTANT

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The rectangular surface of area $8 cm \times 4 cm$ of a black body at a temperature $127 ° C$ emits energy at the rate of $E$ per second. If the length and breadth of the surface are each reduced to half of the initial value and the temperature is raised to $327 ° C$ , the rate of emission of energy will become,

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Important Questions on Heat Transfer

MEDIUM

11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 18 - Heat Transfer>EXERCISE>Q 60

The temperature of the middle (i.e. second) plate under steady state condition, when three very large plates of same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. The first and third plates are maintained at temperatures

2 T

and

3 T

respectively.

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11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 18 - Heat Transfer>EXERCISE>Q 61

Find Rate of flow of heat through copper rod, where three rods of copper, Brass and steel are welded together to form a

Y

-shaped structure. Area of cross-section of each rod

= 4 {cm}^{2}

. End of copper rod is maintained at

100 ° C

whereas ends of brass and steel are kept at

0 ° C

. Lengths of copper, brass and steel rods are

46, 13

and

12 cm

respectively. The rods are thermally insulated from surroundings except at ends. The thermal conductivities of copper, brass and steel are

0.92, 0.26

and

0.12 C G S

units respectively.

MEDIUM

11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 18 - Heat Transfer>EXERCISE>Q 62

The ratio of thermal conductivities of the materials of

P a n d Q

. Same quantity of ice is filled in each of the two metal containers

P

and

Q

having the same size, shape, and wall thickness but made of different materials. The containers are kept in identical surroundings. The ice in

P

melts completely in time

t_{1}

whereas that in

Q

takes a time

t_{2}

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11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 18 - Heat Transfer>EXERCISE>Q 63

The rate of heat absorbed by the body is proportional. A solid maintained at

t_{1} ° C

is kept in an evacuated chamber at temperature

t_{2} ° C (t_{2} > > t_{1})

MEDIUM

11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 18 - Heat Transfer>EXERCISE>Q 64

Two spherical bodies

A

(radius

6 cm

) and

B

(radius

18 cm

) are at temperatures

T_{1}

and

T_{2}

, respectively. The maximum intensity in the emission spectrum of

A

is at

500 nm

and in that of

B

is at

1500 nm

. Considering them to be black bodies, what will be the ratio of the rate of total energy radiated by

A

to that of

B

MEDIUM

11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 18 - Heat Transfer>EXERCISE>Q 65

If the shell now undergoes an adiabatic expansion the relation between

T a n d R .

Consider a spherical shell of radius

R

at temperature

T

. The black body radiation insider it can be considered as an ideal gas of photons with internal energy per unit volume

u = (\frac{U}{V}) \propto T^{4}

and pressure

p = \frac{1}{3} \frac{U}{V}

The rectangular surface of area 8 cm×4 cm of a black body at a temperature 127 °C emits energy at the rate of E per second. If the length and breadth of the surface are each reduced to half of the initial value and the temperature is raised to 327 °C, the rate of emission of energy will become,

Important Questions on Heat Transfer

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